A loop-free network is an essential requirement of Layer-2 networks. As will be understood by those skilled in the art, Classical Ethernet (CE) networks use the Spanning Tree Protocol (STP) whereas Data Center Ethernet (DCE) networks use the Intermediate-System-to-Intermediate-System (IS-IS) protocol to detect and break “steady-state” loops. Preventing “transient loops” (temporary loops caused during network convergence) is an equally important requirement for these protocols. In a hybrid network, consisting of both CE networks and DCE networks, DCE networks generally act as a hub connecting various CE networks together. Accordingly, STP protocol messages sent between different CE networks are tunneled through the DCE network(s) as regular data packets. STP of the CE networks may thus operate to break any overall loops.
However, while both STP and IS-IS function appropriately within their respective networks to prevent transient loops, they are not able to prevent all the transient loops when two DCE networks merge in case of a hybrid topology. In particular, the DCE networks (IS-IS) generally converge after the merge faster than the CE networks (STP), such that any traffic using the newly merged DCE networks between CE networks may be subject to a transient loop (e.g., where the CE networks are themselves interconnected outside of the merged DCE networks) until STP has had a chance to break the loop, accordingly.